This is a clinical trial designed to determine whether high-level, short-term application of fluoride is more efficacious than a low-level, long-term method. A comparison will be made between five minute applications of acidulated phosphate fluoride gel (1.23% F) in custon-fitted trais for ten consecutive school days under dental hygienists' supervision and a one-minute use of fluoride mouthrinse (0.023% F) each school day for the duration of two school years. The comparative effectiveness of these two modes of application would be determined by the dental caries experience of study subjects.